In conventional cellular mobile communication systems, a UE (user equipment) has to communicate with the other UE only through the relaying of base stations regardless of the distance between the two UEs. FIG. 1 illustrates this conventional communication mode, where UE1 and UE2 exchange information through the UTRAN consisting of the base station transceiver (namely Node B) and the RNC, and this communication mode is also called UP-UTRAN-DOWN mode. However, in some case s when the distance between two UEs in the same cell is very close, it can be a more reasonable way for them to communicate directly, rather than through the relaying of base stations. This method is the so-called peer-to-peer communication, abbr. as P2P.
FIG. 2 illustrates a P2P communication mode. As FIG. 2 shows, where the dashed line represents signaling link, the solid line represents data link and the arrowhead represents direction of information flow. Only signaling link exists between the UTRAN and the UE, while only data link exists between the two communicating UEs. Assume that only resource for maintaining basic communication is needed. If a direct link is taken as one unit of radio resource (with fixed frequency, timeslot and spreading code), it can be easily drawn that P2P communication mode only needs two units of radio resource to maintain basic communication. If additional signaling cost for management is ignored, P2P communication can save about 50% radio resource than conventional communication mode. Meanwhile, the UTRAN still holds control over P2P communication, especially over how to use radio resources, so that network operators can easily charge for the radio resource used in P2P communication.
It is commonly accepted that a Time Division Duplex (TDD) air interface is a communication standard that offers a more flexible adaptation to different uplink and downlink traffic requirements. Among existing 3G systems based on TDD communication mode, TD-SCDMA (Time Division—Synchronization Code Division Multiple Access) system is an ideal communication system to be the most suitable for the combination of P2P communication with conventional communication mode, because the same carrier frequency is applied in both uplink and downlink communications, which can simplify the RF (Radio Frequency) module of the mobile terminal.
A method and apparatus for establishing P2P communication in wireless communication networks, as described in the patent application entitled “A Method and Apparatus for Establishing P2P Communication in Wireless Communication Networks”, filed by KONINKLIJKE PHILIPS ELECTRONICS N.V. on Mar. 7, 2003, with the application Ser. No. 03119892.9, is suitable to any TDD CDMA communication system including TD-SCDMA systems, and incorporated herein as reference.
A method and apparatus for radio link establishment and maintenance with P2P communication in wireless communication networks, as described in the patent application entitled “A Method and Apparatus for Radio Link Establishment and Maintenance with P2P Communication in Wireless Communication Networks”, filed by KONINKLIJKE PHILIPS ELECTRONICS N.V. on Mar. 7, 2003, with the application Ser. No. 03119895.3, is suitable to any wireless communication system including TD-SCDMA systems, and incorporated herein by reference.
After establishing uplink synchronization with the UTRAN through the same random access procedure as existing TD-SCDMA systems, the UE can establish a P2P direct link with the other UE, in accordance with the method and apparatus as described in the patent application document whose application Ser. No. is 03119892.9, i.e.: allocate relevant dedicated resource for two P2P UEs. Then, direct link between the two UEs can be established and maintained in accordance with the method and apparatus as described in the patent application document whose application Ser. No. is 03119895.3, so that the two UEs can receive and transmit P2P signals in the allocated timeslots respectively, and thus P2P communication between two UEs can be achieved.
However, in P2P communication mode, the P2P link between the involved UEs or the signaling link between the UE and UTRAN may deteriorate because of the communication environment changing or the movement of the UEs. So a UE in P2P communication mode (abbr. as P2P UE later) has to switch from P2P mode to continue communication in conventional UP-UTRAN-DOWN mode when the P2P link and the signaling link can't satisfy the QoS requirement. A detailed description is offered to the method for switching from P2P communication mode to conventional communication mode, as described in the patent application entitled “A Method and Apparatus for Soft-Switching between P2P Communication Mode and Conventional Communication Mode in Wireless Communication Systems”, filed by KONINKLIJKE PHILIPS ELECTRONICS N.V. on May 19, 2003, with the application Ser. No. as 03123742.8, and incorporated herein as reference.
According to the technical details as disclosed in the above application document, when one or two P2P UEs move to the border of the cell where they camp (the active cell), the signaling link between the UE and the base station (Node B) can't maintain normal P2P communication, so the UEs will first switch from current P2P communication mode to conventional communication mode, and then handover to an adjacent cell that can satisfy the QoS requirement, by using the cell handover method in conventional mode, and continue to communicate in conventional mode.
According to the technical solution of the application document, two UEs can continue communication without being noticed by subscribers, but P2P communication has a remarkable advantage of saving network resource. Hence, when cell handover is needed for P2P UEs, it would be a more reasonable communication mode option that the two UEs to continue P2P communication if they still can satisfy the requirement for P2P communication.